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83 lines
1.7 KiB
83 lines
1.7 KiB
5 years ago
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应用的 UI 线程是怎么启动的？
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1. 什么是 UI 线程？
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2. UI 线程的启动流程，消息循环是怎么创建的
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3. 了解 Android 的 UI 显示原理，UI 线程和 UI 之间是怎么关联的？
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#### 什么是 UI 线程？
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1. UI 线程就是刷新 UI 所在的线程
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2. UI 是单线程刷新的
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UI 线程 == 主线程？
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1. Activity.runOnUiThread(Runnable)
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2. View.post(Runnable)
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```java
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final void runOnUiThread(Runnable action) {
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if(Thread.currentThread() != mUiThread) {
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// Handler mHandler = new Handler();
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mHandler.post(action);
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} else {
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action.run();
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}
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}
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final void attach(Context context, ...) {
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mUiThread = Thread.currentThread();
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}
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```
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对 Activity 来说，UI 线程就是主线程！
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```java
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public boolean post(Runnable action) {
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final AttachInfo attachInfo = mAttachInfo;
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if(attachInfo != null) {
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return attachInfo.mHandler.post(action);
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}
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ViewRootImpl.getRunQueue().post(action);
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return true;
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}
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```
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对 View 来说，它的 UI 线程就是 ViewRootImpl 创建的时候所在的线程！
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```java
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void checkThread() {
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if(mThread != Thread.currentThread()) {
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throw new CalledFromWrongThreadException("");
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}
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}
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```
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Activity 的 DecorView 对应的 ViewRootImpl 是在主线程创建的！
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**关于 UI 线程的三个结论**
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1. activity.runOnUiThread()
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对 Activity 来说，UI 线程就是主线程！
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2. View.post(Runnable r)
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对 View 来说，它的 UI 线程就是 ViewRootImpl 创建的时候所在的线程！
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3. checkThread()
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Activity 的 DecorView 对应的 ViewRootImpl 是在主线程创建的！
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#### UI 线程的启动流程
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1. Zygote fork 进程
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2. 启动 binder 线程
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3. 执行入口函数
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```java
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// ActivityThread#main
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```
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